The invention relates to a method for testing and repairing an injector for injecting fuel into the combustion chamber of an internal combustion engine, wherein the injector includes a nozzle, a restrictor plate, and a control valve, and a nozzle clamping nut which holds together said parts and by way of which said parts are fastened to an injector body of the injector.
In servo-controlled injectors for internal combustion engines and, in particular, in modular common-rail injection systems, injection control is performed by the aid of an electronically actuated control or servo valve. The control valve controls the discharge of fuel from the control chamber of an injection nozzle, which realizes the hydraulic operation of an injection nozzle. By modular common-rail injection systems, injections systems are understood, which are above all used in particularly large engines, in which the individual injectors are sometimes fixed at considerable mutual distances such that the single use of a common rail for the injectors does not make sense. In such engines, it is therefore provided to assign each injector a separate high-pressure fuel storage device integrated in the injector. Such a mode of construction is referred to as a modular structure, since each individual injector has its own high-pressure fuel storage device and can thus be used as an independent injector unit. A high-pressure fuel storage device in this context does not imply just an ordinary line, but a high-pressure fuel storage device is meant to be a pressure-proof vessel having a supply line and a discharge line and whose diameter is considerably enlarged compared to high-pressure lines, in order to enable a certain injection amount to be discharged from the high-pressure fuel storage device without causing an immediate pressure drop, as would happen if the injection amount were taken from an ordinary high-pressure line.
Modular injectors, to which the present invention refers, in addition to the high-pressure fuel storage device integrated in the injector body include a functional group comprising a nozzle, a restrictor plate and a control valve as functional components, which are screwed to the injector body by a nozzle clamping nut. The injection characteristics of an injector in this case are exclusively influenced by the tolerance positions of the above-described functional components. In order to ensure that the injection amounts of the individual injectors fall within a very narrow tolerance band, it will frequently not suffice to produce the nozzle, the restrictor plate and the servo valve within narrow tolerances. In many cases, these three functional components are selectively paired based on specific characteristic features, or individual properties are selectively produced or adjusted only after having measured the other functional components in respect to their functionally critical characteristic features. The correct combination of nozzle, restrictor plate and servo or control valve will thus be decisive for an injector to operate within a very narrow tolerance band.
For the first delivery, the injectors are completely, screwed together and functionally tested on elaborately calibrated test benches during the initial assembly. Injectors that lie outside the set tolerance limits will again be disassembled, one or several functional components will be exchanged, and the injectors will again be screwed together and checked anew. After a defined engine operating time, it is, furthermore, provided to periodically clean and disassemble the injectors, renew the functional components as required, and subsequently mount, and functionally test, the complete injectors as in the case of the first delivery. In the hitherto known test and repair methods, both cases, on the location of manufacture of the injectors, each have involved the handling of partially very heavy injector bodies occasionally weighing 10 kg and more, in addition to the relatively light-weight and small functional components. In the case of repair, the whole injectors with the high-pressure fuel storage devices have to be collected and transported to a central location where they can be repaired.